Methylmercury uptake and degradation by methanotrophs

Xia, Lu; Gu, Wenyu; Zhao, Linduo; Haque, Muhammad Farhan Ul; DiSpirito, Alan A.; Semrau, Jeremy D.; Gu, Baohua

doi:10.1126/sciadv.1700041

Cited by 92 publications

(95 citation statements)

References 45 publications

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“…We have also shown methanobactin can bind methylmercury (99), suggesting that methanobactin can also control its bioavailability. Indeed, we have found that M. trichosporium OB3b takes up and degrades methylmercury (100). This is surprising, as merB, encoding organomercurial lyase, is not present in the genome of M. trichosporium OB3b, indicating that this strain uses another mechanism to demethylate methylmercury.…”

Section: Implications Of Methanobactin-metal Interactionsmentioning

confidence: 87%

Metals and Methanotrophy

Semrau

DiSpirito

et al. 2018

Appl Environ Microbiol

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124

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Aerobic methanotrophs have long been known to play a critical role in the global carbon cycle, being capable of converting methane to biomass and carbon dioxide. Interestingly, these microbes exhibit great sensitivity to copper and rare-earth elements, with the expression of key genes involved in the central pathway of methane oxidation controlled by the availability of these metals. That is, these microbes have a "copper switch" that controls the expression of alternative methane monooxygenases and a "rare-earth element switch" that controls the expression of alternative methanol dehydrogenases. Further, it has been recently shown that some methanotrophs can detoxify inorganic mercury and demethylate methylmercury; this finding is remarkable, as the canonical organomercurial lyase does not exist in these methanotrophs, indicating that a novel mechanism is involved in methylmercury demethylation. Here, we review recent findings on methanotrophic interactions with metals, with a particular focus on these metal switches and the mechanisms used by methanotrophs to bind and sequester metals.

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Section: Implications Of Methanobactin-metal Interactionsmentioning

confidence: 87%

Metals and Methanotrophy

Semrau

DiSpirito

et al. 2018

Appl Environ Microbiol

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124

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“…Two pathways have been proposed for microbial MeHg demethylation: the reductive pathway that first cleaves MeHg to Hg(II) and CH 4 by an organomercurial-lyase enzyme encoded by merB and then to Hg(0) by mercuric reductase encoded by merA of Hg-resistant bacteria (46)(47)(48)(49)(50), as well as by the oxidative pathway that completely oxidizes MeHg to CO 2 and Hg(II) by SRP and methanogens (51)(52)(53)(54). More recently, a methanotroph was also reported to degrade MeHg via the potential activity of methanol dehydrogenase (55). To gain insight into the detailed mechanisms that determine the fate of MeHg, further efforts should be made to assess the expression of hgcAB with the identification of MeHg demethylators and their activities in wetland ecosystems such as the Everglades.…”

Section: Discussionmentioning

confidence: 99%

Periphyton and Flocculent Materials Are Important Ecological Compartments Supporting Abundant and Diverse Mercury Methylator Assemblages in the Florida Everglades

Bae

Dierberg²,

Ogram

2019

Appl Environ Microbiol

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Mercury (Hg) methylation in the Florida Everglades is of great environmental concern because of its adverse effects on human and wildlife health through biomagnification in aquatic food webs. Periphyton and flocculant materials (floc) overlaying peat soil are important ecological compartments producing methylmercury (MeHg) in this ecosystem. These compartments retain higher concentrations of MeHg than did soil at study sites across nutrient and/or sulfate gradient(s). To better understand what controls Hg methylation in these compartments, the present study explored the structures and abundances of Hg methylators using genes hgcAB as biomarkers. The hgcA sequences indicated that these compartments hosted a high diversity of Hg methylators, including Deltaproteobacteria, Chloroflexi, Firmicutes, and Methanomicrobia, with community compositions that differed between these habitats. The copy numbers of hgcAB quantified by quantitative PCR revealed that floc and soil supported higher numbers of Hg methylators than periphyton in the Everglades ecosystem. The abundance of Hg methylators was strongly positively correlated with concentrations of carbon and nutrients (e.g., phosphorus and nitrogen) according to redundancy analysis. Strong correlations were also observed among numbers of sulfate reducers, methanogens, and the dominant hgcAB-carrying groups, suggesting that hgcAB would spread primarily through the growth of those assemblages. The abundances of Hg methylators were weakly negatively correlated to MeHg concentrations, suggesting that the size of this population would not solely determine the final concentrations of MeHg in the ecological compartments studied. This study extends the knowledge regarding the distribution of diverse potential mercury methylators in different environmental compartments in a wetland of national concern. IMPORTANCE Methylmercury is a potent neurotoxin that impacts the health of humans and wildlife. Most mercury in wetlands such as the Florida Everglades enters as inorganic mercury via atmospheric deposition, some of which is transformed to the more toxic methylmercury through the activities of anaerobic microorganisms. We investigated the numbers and phylogenetic diversity of hgcAB, genes that are linked to mercury methylation, in the soil, floc, and periphyton in areas of the Everglades with different sulfate and nutrient concentrations. Soil harbored relatively high numbers of cells capable of methylating mercury; however, little detectable methylmercury was present in soil. The greatest concentrations of methylmercury were found in floc and periphyton. The dominant methylators in those compartments included methanogens and Syntrophobacteriales. This work provides significant insight into the microbial processes that control methylation and form the basis for accumulation through the food chain in this important environment.

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“…SB2 Mbn exhibiting less selectivity for copper (144, 145). A role for Mbn in methylmercury (CH 3 Hg + ) degradation has also been suggested, although Mbn does not demethylate mercury on its own (146). It may be that the ability of Mbn to reduce methylmercury makes the substrate available to the demethylating enzyme (53, 147).…”

Section: Methanobactinsmentioning

confidence: 99%

Chalkophores

Kenney

Rosenzweig

2018

Annu. Rev. Biochem.

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Copper-binding metallophores, or chalkophores, play a role in microbial copper homeostasis that is analogous to that of siderophores in iron homeostasis. The best-studied chalkophores are members of the methanobactin (Mbn) family—ribosomally produced, posttranslationally modified natural products first identified as copper chelators responsible for copper uptake in methane-oxidizing bacteria. To date, Mbns have been characterized exclusively in those species, but there is genomic evidence for their production in a much wider range of bacteria. This review addresses the current state of knowledge regarding the function, biosynthesis, transport, and regulation of Mbns. While the roles of several proteins in these processes are supported by substantial genetic and biochemical evidence, key aspects of Mbn manufacture, handling, and regulation remain unclear. In addition, other natural products that have been proposed to mediate copper uptake as well as metallophores that have biologically relevant roles involving copper binding, but not copper uptake, are discussed.

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Methylmercury uptake and degradation by methanotrophs

Abstract: Certain methanotrophs can take up and degrade methylmercury, signifying a potentially important demethylation pathway in the environment.

Cited by 92 publications

References 45 publications

Metals and Methanotrophy

Metals and Methanotrophy

Periphyton and Flocculent Materials Are Important Ecological Compartments Supporting Abundant and Diverse Mercury Methylator Assemblages in the Florida Everglades

Chalkophores

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